Authentication Protocol Security - Error Packet

(Page 6 of 7 )

When something goes wrong with the processing of a command, the server responds with an error packet. The format is documented in Table 4-9.

Table 4-9. Format of server’s error packet

Offset in the body	Length	Description
0	1	A byte containing 255. The client will always treat a response packet starting with a byte containing 255 as an error message.
1	2	The error code. Low byte first. The field will not be included if the server is talking to a very ancient pre-3.23 client, and the subsequent offsets should be adjusted accordingly in that case.
3	2	Character ‘ # ’ followed by the byte containing the value of the ODBC/JDBC SQL state. Present only in version 4.1 and later.
5 in version 4.1 and later, 3 in 4.0 and earlier	Varies	Zero-terminated text of the error message.

To send an error packet from inside the server, call send_error() , which is defined in sql/protocol.cc in version 4.1 and later, and in sql/net_pkg.cc in version 4.0 and earlier.

EOF Packet

The end-of-file (EOF) packet is used to communicate a number of messages:

EOF) packet is used to communicate a number of messages: The end-of-file (EOF) packet is used to communicate a number of messages:

1. End-of-field information data in a result set
   
2. End-of-row data in a result set
   
3. Server acknowledgment of COM_SHUTDOWN
   
4. Server reporting success in response to COM_SET_OPTION and COM_DEBUG
   
5. Request for the old-style credentials during authentication

The body of an EOF packet always starts with a byte containing decimal 254. In the pre-4.1 era, there was nothing else in the body in addition to this byte. Version 4.1 added another 4 bytes of status fields with the potential of going up to 7 bytes. The format of the version 4.1 EOF body is outlined in Table 4-10.

Table 4-10. Format of server’s EOF packet

Offset in the body	Length	Description
0	1	Byte with the decimal 254
1	2	Number of warnings
3	2	Server status bit mask

The reason for the 7 byte limit in the status bytes area is that the decimal 254 byte followed by an 8 byte string at the beginning of a packet body can have a different meaning: it can specify the number of fields in a result set using the field length format described in the “Data Field ” section, earlier in this chapter.

To send an EOF packet, the server uses send_eof() , which is defined in sql/protocol.cc in 4.1 and later, and in sql/net_pkg.cc in the earlier versions.

Next: Result Set Packets >>
 

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